The present invention relates to a non-constraining device for monitoring the absence of endangered bodies in a swimming pool. There is a presumption and triggering of an alert when monitoring this absence is disturbed.
When a person suffers from an indisposition in a swimming pool as a result of a major problem such as hydrocution, a heart attack, exhaustion etc., the natural reflex of the rachidian bulb causes him to swallow a volume of water the effect of which is to accelerate the body's movement down to the bottom of the swimming pool. Such events can happen when a swimming pool attendant is on duty but could be momentainly absent or simply unable to see the person in difficulty because of reflections of the sun's rays on the surface of the water, or because of an unfavorable angle of vision or simply due to inattention. Likewise, other bathers may be in the proximity without being aware of the problem.
The reaction time is important and each few seconds before an alert is given can be decisive for the person in danger.
Several solutions have already been proposed to resolve this problem. However, the different known equipments are based essentially on the use of sonar or radio waves or even laser beams and are relatively ill-adapted to use in public swimming pools due to difficulties related principally to the properties of the water or reflective effects against the walls.
FIG. 2 presents the coefficients of absorption of electromagnetic waves measured in pure water. On the abscissa, is the wavelength wherein the zone of visibility is in the region of 0.35 to 0.8 micrometers. On the ordinate is the attenuation per centimeter of water traversed. By way of indication, the attenuation over 10 m of water at a wavelength of 0.8 microns, at the border of visible infra red, is 0.000043. Moreover, low attenuation coefficients corresponding to the blue-violet zone are substantially altered by the water's turbidity when many bathers are swimming. By way of example, when a swimming pool is observed through portholes while the pool is densely occupied, it may be difficult or even impossible to distinguish a bather located at 25 or 30 m.
U.S. Pat. No. 5,043,705 is written in very general terms and is based on the measurement of the distance between the detector and a possible obstacle to ascertain its presence. It mentions various components including a sonar adequately adapted to detect a body placed between the sonar and a wall, but which would encounter enormous difficulties to detect a body situated very close to a wall, the latter creating numerous reflections. The same applies to detection by radio frequency due to problematic propagation in water. This patent also mentions lasers without however specifying the mode of operation. Moreover, it enumerates general methods of eliminating noise because its aim is the identification of the immobile object.